Composites of elastic and non-elastic material have been made by bonding the elastic material to the non-elastic material in a manner that allows the entire composite to stretch or elongate. Often these composites are used in garment materials, pads, diapers adult incontinence products, feminine hygiene products and the like. One such composite or laminate includes an extensible nonwoven material bonded to an elastomeric sheet.
However, such laminates make inefficient use of the elastic resins that are included in the elastomeric sheet. Generally, hysteresis and elasticity are inversely related. In other words, if a material has a higher hysteresis value it will be less elastic and if the material has a lower hysteresis value it is more elastic. Films made from the resins and compounds typically chosen for use in these laminates have a hysteresis value between about 25 percent and about 50 percent as measured using a 100% cycle test. In contrast, laminates made with these same films typically have hysteresis values between about 50 percent and about 75 percent as measured using a 100% cycle test. This is likely due to the interactions between the extensible nonwoven material and the elastomeric sheet, which is dependent on the level of attachment between the layers of the laminate.
Generally, the more attachment there is between the extensible nonwoven material and the elastomeric sheet, in terms of the number of bonds and/or the intensity or strength of the bonds, the worse the elastic properties of the laminate. Ideally, the attachments between the extensible nonwoven material and the elastomeric sheet should be sufficient to keep the layers of the laminate together but not unduly affect the elastic properties of the laminate.
When an extensible nonwoven web is laminated to an elastomeric sheet at least two types of bonds are typically formed between the webs: primary bonds and secondary bonds. Primary bonds are intentionally formed, are stronger and work to maintain the internal cohesion of the laminate such that when the laminate is stretched or elongated the layers do not separate from each other. Secondary bonds, on the other hand, are weaker and can be broken to a large extent during a first extension/relaxation cycle. As a result of the formation of these secondary bonds, the laminate is less elastic and more difficult to stretch particularly the first time the laminate is stretched. Generally, it is believed that the first stretch of the laminate causes the filaments of the extensible nonwoven material in the secondary bonds to cut through and/or detach from the elastomeric sheet. The required energy to cut through and/or detach these bonds is, in general, non-recoverable. Non-recoverable energy causes an energy loss or an increase in hysteresis.
Additionally, unstretched elastomeric sheets typically have poorer stretch properties during the first elongation/retraction cycle because the molecules making up the sheet are relatively non-uniformly or randomly oriented within the sheet. The required energy to orient the molecules, like that required to detach the secondary bonds, is, in general, non-recoverable and can also contribute to an increase in hysteresis.
In most instances, these laminates are included in consumer products without having been previously stretched. Thus, when a consumer uses a product including such a laminate they must exert more force to extend or elongate the laminate in order to achieve proper fit and comfort. Also, because the laminate has not been previously stretched it may stretch unevenly or discontinuously, especially if a non-uniform force is applied. This results in discomfort to the wearer and poor fit of the product as well as poor subsequent stretching of the laminate while in use.
With the foregoing in mind, there is a need or desire for an extensible laminate that makes efficient use of the stretch properties of the elastic film component. There is also a need or desire for an extensible laminate that a consumer may easily and uniformly stretch to provide better fit and more comfortable wear of a consumer product including the extensible laminate.
It is a feature and advantage of the invention to provide an extensible laminate that may be utilized in a consumer product to provide better fit and comfort. It is also a feature and advantage of the invention to provide a method for making an extensible laminate having improved stretch properties.